How gels and gelling agents work

[CrimpJiggler]

I'm trying to learn what exactly gelling agents are, what they do and how they do it. A good place to start would be to learn what gels are, I read the wikipedia page on gels:
https://secure.wikimedia.org/wikipedia/en/wiki/Gel
and am pretty fascinated now. So gels are actually mixtures containing a solid skeletal structure which completely ensnares liquid inside its 3D structure? I assume then that gelling agents are the solid compounds that do the ensnaring. I notice that all the gelling agents I've heard of so far are polymers but I just came across this article:
http://findarticles.com/p/articles/mi_qa5350/is_200309/ai_n21336329/
which talks about small, low molecular weight gelling agents so I see now that its not just long chained polymers that can form these 3D cages for liquids. I can't find enough info on the chemistry of gels and gelling agents to get my head around the whole concept so I'll have to ask some questions. I read there that those novel low MW gelling agents hold the 3D cage together with weak intermolecular forces while classical gelling agents hold it together with covalent bonds. Are the classical gelling agents all polymers? If so do they have to be highly branched to act as gelling agents?

 

[jbsteele]

Also, how can the same molecule act as a gelling agent in some cases and not in others? Gelling agents are substances that form a gel, which is a type of colloidal suspension in which a liquid is trapped within a 3D network of polymers or small molecules. The most common gelling agents are polymers, such as polysaccharides, proteins, and synthetic polymers. These polymers form the 3D network by either covalent bonds between the polymer chains, or by weak intermolecular forces between the molecules. Depending on the type of molecule used to form the gel, the strength of the gel will vary. For example, polysaccharides form relatively weak gels, while synthetic polymers form stronger gels.In some cases, small molecules can act as gelling agents. These molecules form the 3D network by weak intermolecular forces, such as hydrogen bonds and van der Waals forces. These gels tend to be weaker than those formed by polymers, but they can still be useful in certain applications.The same molecule can act as a gelling agent in some cases and not in others depending on the environment in which it is used. For example, a polymer may form a gel in an aqueous solution, but may not form a gel in an organic solvent. Similarly, a small molecule may form a gel in an organic solvent, but may not form a gel in an aqueous solution.